As well known, an optical fiber characteristic measuring device uses an optical fiber itself as a sensor by making continuous light or pulse light incident to the fiber and receiving scattering light or reflected light generated in the fiber. Hitherto, various types of optical fiber characteristic measuring device have been proposed. As the scattered light received by the optical fiber characteristic measuring device in order to measure the characteristics of the optical fiber, the optical fiber characteristic measuring device uses Rayleigh scattering light, Brillouin scattering light, Raman scattering light, or the like; as the reflected light it uses Fresnel reflected light or the like.
Patent Document 1 below discloses an optical fiber characteristic measuring device that makes frequency-modulated continuous lights (pump light and probe light) incident to an optical fiber from both its ends, forming a cyclic correlation peak of the pump light and the probe light along the optical fiber, and measures the characteristics of the optical fiber by utilizing characteristics that probe light is amplified only at the correlation peak by stimulated Brillouin scattering phenomenon. This optical fiber characteristic measuring device varies the position of the correlation peak in the optical fiber while receiving the probe light amplified at each position, and thereby measures characteristics in the long direction of the fiber.
Patent Document 2 below discloses an optical fiber characteristic measuring device that makes frequency-modulated continuous light (probe light) and pulse light (pump light) incident respectively to one end and the other end of an optical fiber, sequentially generates correlation peaks in accordance with the position of the pump light propagating in the fiber, and, of the light emitted from the optical fiber, obtains only the light (stimulated Brillouin scattering light) from near the measuring point, and thereby measures the characteristics of the fiber near that measuring point. This optical fiber characteristic measuring device moves the measuring point by adjusting the modulation frequency of the probe light and the pump light, and the timing of receiving light emitted from the fiber, whereby it can measure the characteristics at a given position in the long direction of the fiber.
The optical fiber characteristic measuring device disclosed in Patent Document 2 sweeps the optical frequency-difference between the pump light and the probe light while measuring the optical power of the stimulated Brillouin scattering light generated at the correlation peak position, and detects the peak frequency, whereby it can measure the size of the strain and the temperature at that position.    [Patent Document 1] Japanese Patent Publication No. 3667132    [Patent Document 2] Japanese Patent Publication No. 3607930